One common method for printing images on a receiver material is referred to as electrophotography. The production of black-and-white or color images using electrophotography generally includes the production of a latent electrostatic image by uniformly charging a dielectric member such as a photoconductive substance, and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern with a desired image. Such discharge is generally accomplished by exposing the uniformly charged dielectric member to actinic radiation provided by selectively activating particular light sources in an LED array or a laser device directed at the dielectric member. After the imagewise charge pattern is formed, it is “developed” into a visible image using pigmented or non-pigmented marking particles (generally referred to as “toner particles”) by using either the charge area development (CAD) method or the discharge area development (DAD) method, which marking particles provide an opposite charge to the dielectric member and are brought into the vicinity of the dielectric member so as to be attracted to the imagewise charge pattern.
Thereafter, a suitable receiver material (for example, a cut sheet of plain bond paper) can be brought into juxtaposition with a toner image that has been formed with the toner particles in accordance with the imagewise charge pattern on the dielectric member, either directly or by using an intermediate transfer member. A suitable electric field is applied to transfer the toner particles to the receiver material in the imagewise pattern to form the desired print image on the receiver material. The receiver material is then removed from its operative association with the dielectric member and subjected to suitable heat or pressure or both heat and pressure to permanently fix (also known as fusing) the toner image (containing toner particles) to form the desired image on the receiver material.
Plural toner particle images of, for example, including colored toner particle images, can be overlaid with multiple toner transfers to the receiver material, followed by fixing all toner particles to form a multi-color image in the receiver material. Toners that are used in this fashion to prepare multi-color images are generally Cyan (C), Yellow (Y), Magenta (M), and Black (K) toners containing appropriate dyes or pigments to provide the desired colors or tones.
Porous polymeric particles have been prepared and used for many different purposes including the use as toner particles. In addition, porous particles have been described for use in chromatographic columns, ion exchange and adsorption resins, drug delivery devices, cosmetic formulations, papers, and paints. The methods for generating pores in polymeric particles are well known in the field of polymer science. However, each type of porous particle often requires unique methods for its manufacture.
Chemically-crosslinked elastomeric porous particles have been prepared for laser-engraveable compositions comprising such particles dispersed within a laser-engraveable elastomeric resin. The presence of these porous particles, which can include an infrared radiation absorber, improves various imaging and performance properties in the preparation of flexographic printing members such as flexographic printing plates and printing sleeves.
In the early days of electrophotographic printing, toner particles were relatively large (for example on the order of 10-15 μm). As a result, the print image had a tendency to exhibit a relief appearance (that is, a variably raised surface). Under most circumstances, the relief appearance was considered an objectionable artifact in the printed image. In order to improve image quality and to reduce the relief appearance, smaller toner particles (less than 8 μm) have since been prepared and used more commonly.
In recent years, there has been a desire to provide multi-dimensional or raised relief toner images so that text or shapes can have a relief appearance that is useful for various purposes. For such purposes a large particle toner having toner particle sizes on the order of greater than about 20 μm or larger is beneficial. In particular, such large particle toners allow larger toner stacks to be created to allow the formation of relief patterns on a substrate.
The desire to use larger toner particles for making multi-dimensional images comes from the interest in generating relief patterns in a way that achieves maximal applied height in a single pass through a printing module.
U.S. Pat. No. 7,965,961 (Priebe et al.) describes electrophotographic printing a raised multi-dimensional toner shape on a receiver member using predetermined sized toner particles such as substantially larger size or alternatively utilizing predetermined sized toner particles having predetermined properties. For example, FIG. 5 of the noted patent illustrates a multi-dimensional toner shape in an image using stacks of the same specific sized toner particles in a particular packing density. Moreover, in FIG. 7, multi-dimensional toner shape is provided in an image using stacks of different sized toner particles to result in greater packing of the toner particles.
U.S. Patent Application Publication 2011/0200360 (Tyagi et al.) describes a method and related apparatus for producing electrophotographic prints with raised letters with height in excess of 100 μm but achieving the raised letter height by multiple applications of toner particles and fusing.
Moreover, U.S. Pat. No. 8,147,948 (Tyagi et al.) describes a method for providing electrophotographic images using a first toner image using relatively small first toner particles followed by printing a second toner image using relatively large second toner particles. U.S. Patent Application Publication 2012/0100479 (Aslam et al.) describes similar methods.
Raised electrophotographic toner images are also provided using multiple layers of small toner particles as described in U.S. Patent Application 2011/0200933 (Tyagi et al.).
While the described methods have provided improvements in the art, there is a need for further improvement. Many of the known methods require multiple passes in the electrophotographic imaging apparatus (multiple formation of toner images) to achieve the desired toner image height. In particular, it will be understood that larger toner particles are difficult to transfer causing toner images made with larger particles to have poor resolution and high granularity. One reason for this is that the Coulombic repulsion between large toner particles causes such larger toner particles to fly apart during transfer thus degrading image quality. This effect is known in the art as dot explosion. In addition, it will be appreciated that the amount of large diameter toner particles that can be developed is limited due to higher charge levels required to transfer such large diameter toner particles. Such challenges associated with transferring large diameter toner particles limit the amount of large diameter toner particles that can be transferred during a single pass and also causes a lack of coherency in the large diameter toner particles that are transferred. These effects, in turn, limit the height of a toner stack that can be formed using large diameter toner particles in a single toner transfer operation. In addition, an image consisting of many toner layers can be difficult to fuse completely, leading to toner offset in the press, cohesive failure somewhere within the toner stack, or marginal-to-poor adhesion of the fused toner image. High toner stacks, coupled with incomplete fusing, can also be prone to brittle fracture (due to poor cohesive strength) when the image is flexed or bent slightly. It is therefore desirable to provide a toner that can have limited toner melt flow by controlling deformation under fusing pressure thereby maintaining stack height and minimizing the number of passes through the imaging apparatus required to get the desired stack height in order to enable the creation of relief patterns. Such raised patterns can be used for any number of structural or aesthetic purposes, including but not limited to providing areas with distinct tactile feel on an image, for creating Braille texts, for providing containment structures for example for fluids, for forming structural and optical elements on the surface of a receiver element. In addition to using multi-dimensional imaging for decorative accents in greeting cards and specialty printing applications, it can be useful for preparing corrugated board by fusing together stacks of regular paper printed with such toners in a cross hatch pattern and for making card stock from standard papers useful as receiver elements. Further, it is desirable to allow the creation of such relief images that are more resilient to bending and flexing.